X on TV

From the Xserver's point of view a TV with a RGB SCART input is nothing but
a fixed sync monitor with a rather low picture quality. This means that you
can make a TV compatible signal with a plain vanilla cheapo VGA card.

Modelines

For the European 625 line (575 visible lines) TV standard a modeline looks
like this:
Modeline "736x575i" 14.16 736 760 824 904 575 580 585 625 interlace -hsync
-vsync
Officially the horizontal resolution is 767 (4 / 3 * 575) pixels with a
clock of 14.76 MHz. However, since the clock used is 14.16 MHz, I reduced
the horizontal values proportional to 14.16 / 14.76 (and rounded them to
the nearest multiple of 8).
14.16 MHz / 904 yields a horizontal deflection frequency of 15.664 kHz,
which should work on most EU (15.625 kHz) (and US, 15.75 kHz) TV's.
If your VGA card's clock is different from 14.16 MHz, you need to change
the horizontal values.

You can probably use the following modeline for the US 525 line (485
visible lines) standard:
Modeline "736x485i" 14.16 736 760 824 904 485 491 496 525 interlace -hsync -vsync

If you want to make a 640x480 screen with a black border you can you use
this line:
Modeline "640x480i" 14.16 640 712 776 904 480 532 537 625 interlace -hsync
-vsync
You can centre it by altering the 2nd and 3rd horizontal and vertical
values (this example shifts the picture to the left):
Modeline "640x480i" 14.16 640 728 792 904 480 532 537 625 interlace -hsync -vsync

More information on the X Window system

Hardware

The VGA RGB signals are compatible with the SCART bus, the sync signals
are not. You have to create a composite sync signal of 0.3 ... 0.5 Vpp.
The circuit below acts both as a AND gate and a level translator.
It doesn't need a power supply and can be mounted inside a VGA plug:

The R-, G- and B grounds are in fact shields (The R-, G- and B wires are in
fact little coaxes). The same goes for the `-CS' wire.

The connector shells are connected to a common shield screening all wires and
coaxes inside the cable.

If you use a female SCART connector, use pin 19 for -CS.

Use

There are several ways to tell your TV to use the RGB Scart input.
In some cases you can use the remote control for this purpose.
Some TV's have a switch near the Scart plug.
In some cases however, you will have to force pin 16 high. A voltage of
0 ... 0.3 V represents off, while a voltage of 0.9 ... 3 V tells the TV to use
the RGB Scart input.
Warning: A voltage > 3 V on pin 16 might damage your TV!

Problems

Apparently, some hardware doesn't support interlaced mode. If you have
sync problems, check the sync signal with an oscilloscope.